Described in U.S. Pat. No. 4,921,008 (corresponding to Australian patent 597625) is a valve that is inserted in a flow line to prevent flow should there be a rupture downstream of the valve. Typically the valve of this USA patent is employed with a pressurised gas cylinder that provides gas to, for example, a stove or other appliance that uses the gas. Should there be a failure downstream of the valve, the valve is actuated to prevent further gas flowing from the cylinder.